Conventionally, a linear solenoid is used for a solenoid oil-pressure control valve (i.e., solenoid hydraulic control valve). The linear solenoid includes a coil assembly, a cup-shaped yoke, a plunger and a stator. The coil assembly includes a coil which generates a magnetic force when being energized, and the cup-shaped yoke is arranged outside of the coil to pass therethrough magnetic flux. The plunger is arranged slidably at an inner peripheral side of the coil assembly, and the stator is disposed to attract the plunger by the magnetic force generated when electrical current is applied to the coil.
The yoke is provided with an open portion through which a terminal connected to an exterior equipment leads out so as to supply an electrical power to the coil.
The linear solenoid used for the solenoid oil-pressure control valve is generally provided at a position to which oil with a foreign material is easily sprinkled. Thus, the foreign-material mixed oil may be introduced into the yoke from the open portion that is provided for the terminal, and may stay inside of the yoke. If the foreign-material mixed oil stays inside of the yoke, the foreign-material mixed oil may reach to the plunger, and thereby sliding performance of the plunger may be affected. Thus, it is required to restrict the foreign-material mixed oil from being introduced into the yoke from the open portion.
In Patent Document 1 (JP 2005-315316A), an open portion for a terminal (i.e., terminal window) is provided at a bottom wall of a yoke and is covered by a cover from an outside of the yoke, so as to prevent foreign-material mixed oil from flowing into an inside of the yoke.
However, in Patent Document 1, because the cover is provided separately from the yoke, the structure of the linear solenoid becomes complex, thereby increasing the cost. Furthermore, the linear solenoid of Patent Document 1 does not have a function for discharging the foreign-material mixed oil to outside of the yoke after the foreign-material mixed oil is introduced once into the yoke. Thus, the foreign-material mixed oil may continuously stay in the yoke after being introduced into the inside of the yoke.